This invention relates to compositing pages from page components.
To print an image, a page of text and graphics, for example, the image typically is sent to a print engine from a frame buffer as a rasterized set of pixel values. The original image data from which the rasterized pixel values are generated are often in a compressed format, which must be decompressed for use by the print engine.
The original compressed image data may be stored in a file that describes elements of the image and their interrelationships. For example, the image elements may include a background layer and foreground text and graphic elements that appear overlaid on the background. Converting such a page description to a final rasterized data set is called compositing.
Sometimes it is useful to print personalized pages, for example, pages that have image elements in the foreground that differ from page to page, and other image elements in the background that are shared in common from page to page. If such pages are to be printed one after another, the computer typically repeats the entire compositing process or else changes groups of pixels in the frame buffer from page to page.
The process of generating personalized pages can be made faster using two frame buffers, one for a background layer of common elements, the other for the foreground layer of personalization elements. The pages are composited from the two frame buffers. By personalization, we mean, e.g., printing a large number of pages, which are alike in many respects and individually customized in others. For example, each page could have the same advertisement but a different mailing address and perhaps coupons targeted to the demographics of the intended recipient. To minimize storage requirements it is useful to store the elements of the page once and to composite the different pages in real time, as the pages are printed.
Page compositing can be accelerated by using a dedicated processor to decompress the elements of the page (contexts) and composite them in real time into a series of scan line data sets.